The present disclosure relates to an imaging element, an image pickup apparatus, a manufacturing apparatus and a manufacturing method, and particularly to an imaging element, an image pickup apparatus, a manufacturing apparatus and a manufacturing method capable of accurately detecting a black level reference value.
In general, an image pickup apparatus used for a digital camera and a camcoder has an effective pixel region in which pixels outputting signals for forming an image and pixels shielded from light beams by a light shielding film, that is, optical black (herein after abbreviated as OB (Optical Black)) pixels. Because an output signal from the OB pixel serves as a dark signal reference, it is preferred that the OB pixel has a dark current equivalent to that of the effective pixel and deviation of the output signal caused by incident light beams in the image pickup apparatus does not occur. In the video camera and the digital still camera, an imaging element such as a CCD (Charge Coupled Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor is widely used.
Sensitivity improvement is an important issue common to those imaging elements, and sensitivity improvement technology by using a back side illumination CMOS image sensor was developed as one solution (See e.g., Japanese Patent Laid-Open No. 2009-176951).
In the back side illumination CMOS image sensor, the OB pixels are formed on the outer side of an effective pixel region like a front side illumination CMOS image sensor and the same sensor structure as that in the effective pixel region is used except shielded by a light shielding film. And a dummy pixel region is generally formed between the OB pixels and a peripheral circuit for the purpose of figure uniformity of a color filter and a condenser lens.
However, in the back side illumination CMOS image sensor, diffraction of long wavelength light beams is prone to occur in the OB region because of its structure. In the case of the front side illumination CMOS image sensor in the past, because a Sub substrate region existing deeper than a silicon (Si) photoelectric conversion region has a sufficient film thickness, it was unlikely that long-wavelength-band incident light beams enter the OB region. On the other hand, in the case of the back side illumination CMOS image sensor, because a silicon (Si) film thickness of the photoelectric conversion region is thin, the incident light beams were prone to be repeatedly reflected among an Si-wiring layer interface, a wiring and a further lower layer until photoelectrically converted.
During being reflected, because a certain amount of the light beams is incident in the OB region, long-wavelength light beams were likely to be incident at higher rate in the OB region in the back side illumination CMOS image sensor in comparison with the front side illumination CMOS image sensor.
When long-wavelength light beams enter the OB region and electrically converted, black level false recognition is likely to occur to cause a coloring defect in an image, so that it is desirable to reduce the incident light beams as much as possible.
Various technologies have been devised in order to inhibit unnecessary charge from entering the OB pixel to stabilize an output signal of the OB pixel when light beams are incident. In one of the technologies, formation of the OB pixel without detecting unnecessary light beams with maintaining the level of the dark signal reference by reduction of area of the photoelectric conversion region of the OB pixel, that is, reduction of sensitivity was suggested (See e.g., Japanese Patent Laid-Open No. 2006-344888).